Many industrial operations generate fluoride-containing wastewater. For example, even though the process of generating green photovoltaic (PV) electricity from solar cells creates no pollution or waste, the manufacture of solar cells can produce serious pollutions. The fluoride-containing wastewater accounts for a very large percentage of the total hazardous wastes generated in crystalline silicon solar cell manufacturing. The fluoride-containing wastewater must be treated to comply with the industrial effluent discharge standards. For clarity, the following description may use the production of crystalline silicon solar cells as an example to illustrate the invention. However, one skilled in the art would appreciate that embodiments of the invention can also be used with fluoride-containing wastewater generated in other operations.
Crystalline silicon solar cells are made from thin silicon wafers or slices, and the manufacture process consists of six main steps, viz, cleaning, texturization, emitter formation, antireflection film deposition, metallization, and cell testing, as shown in FIG. 1. These six steps are briefly described as follows: